Higher capacity optical links (e.g., 20 GHz to 30 GHz) place greater demands on directly modulated diode lasers. Wavelength division multiplexing provides some relief for these demands. Newer diode lasers are more stable and exhibit narrower linewidths that make coherent optical communications more practical to implement. But, increasing demands for data continue to present problems in optical communications. And, these newer technologies are not always feasible to implement.